Middlings purifier



Oct. 28, 1952 c. nmonmsou MIDDLINGS PURIFIER 5 Sheets-Sheet Fiied Aug. 12, 1949 253 mm uu 5o on 12:66 2.

INVEN TOR CREIGHTON H. MORRISON A T TORNE Y Oct. 28, 1952 c. H. MORRISON MIDDLINGS PURIFIER 3 Sheets-Sheet 2 Filed Aug. 12, 1949 INVE NTOR Y CREIGHTON H. MORRISON BY jazz; C. W

ATTORNEY Oct. 28, 1952 c, M RRI N 2,615,570

MIDDLINGS PURIFiER Filed Aug. 12, 1949 3 Sheets-Sheet 5 FIG.4

I T0 0.0. men

VOLTAGE SOURCE I INVENTOR CREIGHTON H. MORRISON ATTORNEY Patented Oct. 28, 1952 MIDDLINGS PURIFIER Creighton H. Morrison, Minneapolis, Minn., as-

signor-to GeneraliMills, Inc., acorporation'of Delaware Application August 12, 1949, Serial No. 109,886

:23-Claims. '1

The present application relates to electrostatic separation and more particularly to animproved apparatus for electrostatic separation of cereal stocks.

Electrostatic separators have-been proposed in the'past in which'the'stockjto be separated is'fed downwardly along a smooth inclined plate beneath an upper electrodeof theVenetian blind type. Such an'upper electrode includes a series of transverse strips which are spaced slightly from 'each other to provide openings through which the attracted particles may 'pass to the upper surface of the electrodes. These strips, are inclined at an angle which feeds the attracted particles downwardly from one strip to the'next on'the upper surfaces ofthe strips under the-infiuence of gravity.

With these constructions of the-prior art, two separations have been possible. One group of particles may be attracted through'the spaces between the strips of the upper electrode and removed separately as they are fed down the upper surfaces of the strips. The remaining particles continuelto pass 'downfthe lower inclined plate to a point of removal. .Asfaras I am aware, such devices have not'been applied successfully to the separation .of materials in which both particles to be segregated are"non-conductors. Furthermore, such devices have not permitted precise and accurate separations on a commercial scale.

With these defects of'the prior art in view, it is accordingly one objectof the present invention to provide animproved electrostatic separator of the inclined parallel electrode type.

It is a further objecttqprovidean electrostatic separator of this type in -which .the-upperelectrode is provided with openings or perforations and in which a three-fold separation ismade possible.

Another object .is the provision of .an electrostatic separatorof this general type in whichthe lower or supporting electrode. is of. novel and improved construction.

Still another objectof the invention is the provision of such a separator in whichithe inclined supporting or conveyingv electrode is provided with a series of' transversely extending stepsor corrugations.

A further object is'the provision of an electrostaticseparator of this general type in which a corrugated or stair step supporting electrode.is combined with a perforated or .Venetianblind type of upper electrodenandnin .which ;the electrodesiare. subjected :to: vibratorygaction, :durin the feeding. of the; material. between them.

. mang r.- e ei ie ie *2 Other objects and advantages willbe apparent from the followingspecification, in which a preferred embodiment ofthe inventionhasbeen described with particular reference to the accompanying drawings.

In these drawings, wherein like reference characters indicate'likeparts',

Figure 1 is a partial perspective view of an electrostatic separator embodying features of-the present invention.

' tails of theelectrodeconstruction.

The separatorincludes a. base It, at one end of wh is m unted, e ti al fill po iiin Wa l Abracket I4 at'the topoithe supporting wall 12 includes supporting arms [6 on which'ahopper aesignated eneral v at. v lii rmielte A sh wn inFig. .2, the bottom wall jo. of hopper I 8 is inclined downwardly awjayffrom the wall l2 and terminates ina transverse feeding ed ge 2 2 from which thev ma eria lath ho e cab b d ppe tov th spac b ween the; electrodes. The rront wall; 24 of the feed hopper gl .8- carries.at'itsupper edge a supporting bracket Zfi. 'IjlreadedrodsR pa hrou h th su reme attached tq rmoliab q lel $1 arran e wee sate for-the-heppe .t-N lt 3 9 threaqeds ports. .28yperm t- Yerti a'lia Justmen rof h fiee pl e 30 sex tha it .-..1.Q,W ed r. mawbaae curately p s t one at apr d ns ed siene away, from. the..hottom, .plate I hopper. l8;;,to obtain the desiredr uniform L rate of feed of the material from the hopper.

-'Inorder to assist uniform ..feeding ...of .the-

ture .42 so as to. vibrate th dis il emig 3 taining uniformity of feed from the hopper I8 may be utilized in place of the vibrator 36.

The material to be separated is deposited uniformly from the feed lip 22 of hopper 18 onto the lower electrode 50 of a pair of parallel inclined electrodes. Above the electrode 50 is an upper electrode 52 which is spaced from the lower electrode a distance which is relatively small as compared to the length of the electrodes in the direction of feed. Thus the material deposited on the lower electrode 50 will move downwardly along the length of this electrode and will thus pass through the electrostatic field which is established between the electrodes.

The two electrodes 50 and 52, which are metallic, are mounted on insulating side plates 54 and 55 respectively, which in this particular case are made of transparent plastic material in order that the action of the electrostatic field on the material to be separated may be more readily observed. Side plates 54 and 55 are carried by a horizontal supporting plate 51. The lower metallic electrode 50 includes a metallic rear supporting wall 58 and metallic supporting side walls 68. Side walls 88 are fastened by bolts 62 to the insulating side supports 54 and 56. One of the bolts 62 is connected by a suitable wire 64 to the desired potential source, in this case to ground.

The upper electrode 52 is provided with metallic side flanges 66 which have longitudinal slots 68 therein. Bolts I8 pass through the slots 58 in the electrode flanges 86 and also through slots I2 in the insulating side supports 54 and 55. Slots I2 are substantially perpendicular to the plane of the electrode and also to the slots 68. This combination of perpendicular slots in the electrode fiange 66 and side supporting plates 54 and 56 therefore permits adjustment of the upper electrode both toward and away from the lower electrode plate 58, in order to vary the spacing between the electrodes, and also in a direction longitudinally of the electrodes or parallel to the direction of feed. A wire 14 is connected at one end to one of the bolts I8 and at its other end to a suitable direct current high voltage source in order to apply the desired potential to the upper electrode. The difierence in potential between the electrodes accordingly establishes an electrostatic field between electrodes 50 and 52 of a strength which depends on the difference in potential and on the relative separation of the members.

The specific construction of the electrodes is shown best in Figs. 2 and 3. The upper electrode 52 includes a series of transversely extending strips I6 which are inclined downwardly in the direction of feed and which are staggered so as to leave openings between them somewhat in the nature of a Venetian blind. Strips I8 may include a substantially vertical rear wall section or riser I8 leaving openings 80 between the upper edge 82 of the vertical wall portion and the extreme lower edge 84 of the transverse strip I which is immediately above the vertical wall portion I8. Thus the openings 80 permit the passage of particles of material which are attracted from the lower electrode 50 and which can therefore be removed from the electrostatic field between the electrodes and conveyed downwardly on the upper surface of the inclined transverse strips I6 as shown particularly in Fig. 3.

Because of the staggered or overlapping arrangement of the transverse strips IE it is apparent that the field near the upper electrode 52 will not be absolutely uniform as it would be in the case of a flat plate parallel to the lower electrode. Instead, the field will be concentrated somewhat at points 86 where the upper edge of each transverse strip I6 meets the vertical rear wall or riser 78.

In previous electrostatic separators of this inclined Venetian blind type, the lower or supporting electrode 58 has been in the form of a fiat inclined plate. According to the present invention, the lower electrode 50 is provided with a series of steps or corrugations. These steps include the downwardly inclined conveying portions 88 which may be substantially parallel to the transverse strips I6 of the upper electrode and are inclined downwardly to promote the how of the material down the lower electrode 50. The successive conveying steps 88 are separated by risers 90 which are substantially perpendicular to the step portions 88. The lower portion of each riser 98 meets the step portion 88 which is below it, at a line of intersection 92, and also meets the step portion 88 of the step above it along a line of intersection 94. While this lower stair step electrode 58 is substantially parallel to the upper electrode, it will be apparent that the steps or corrugations will not establish an absolutely uniform field between the upper and lower electrodes. Instead, the field adjacent the lower electrode will tend to be concentrated at the end 94 of each step.

At the end of the lowermost or bottom step 88, the electrode 58 has an extension projecting downwardly and rearwardly as shown at 96, in a direction which in this case is substantially perpendicular to the general plane of the electrode itself. Thus a discharge edge 98 is provided at the end of the bottom step.

It should be noted that the upper electrode extends beyond the discharge edge 98 of the lower electrode in the direction of feed of the material. The electrostatic field between this final discharge edge 98 and the upper edge 86 of the last transverse step I6 is the last of a series of relatively intense electrostatic fields through which the material passes at the edge of each successive step. Since the extension 96 of lower electrode 58 diverges from the final step I6 of the upper electrode 52 beyond the discharge edge 98, the electrostatic field between the upper and lower electrodes will decrease in intensity beyond this point. The field will also tend to be more nearly horizontal, due to the diiferent angular orientation of the extension 96, rather than perpendicular to the general plane of the electrodes 58 and 52 as is the case throughout the remainder of the field.

At the lower end of the electrodes 58 and 52 suitable dividers and conveying chutes are provided to remove the material which is separated by themachine. A collecting plate I is mounted at a rather sharp incline below the discharge edge 98 of the lower electrode. This collecting plate IE0 is fastened to a conveying chute I82 at I84. The material received by the plate I80 and chute-I82 is deposited in a suitable receptacle I86. For convenience an ordinary boxlike receptacle has been shown, although it will be understood that this receiving receptacle I could also be the hopper of a subsequent separating unit or could be a suitable chute for feeding material in the desired manner and direction.

An intermediate'dividing plate I88, which may be made of insulating material, extends into the edge of the diverging electrostatic field between aeiasro':

the machine. As shown in Fig. 1, the shaft 2- is provided at its outer end withan adjusting arm H8. A bolt I20 passes through the locking arm and through an arcuate slot I24 ina flange I26 on auxiliary frame HE. A suitable loch-iiut I22 on the locking bolt I20'may be tightenedte retain the adjusting'arm Il8'in any desired position along the extentor the arouate slet I24. Thusthe chute member I Ill'and dividerplate I08 may be rotated by means of shaft II2 to] adjust their position at the lower edge ofthe e1eotrostatic field. -Counterclockvvlse rotation of Shaft II2, as seen in Fig. 2, win lower the divider Ita toward the collecting plate I00, while clockwiserotation of shaft I I2 will shift the divider I08 upwardly to a point near the plane of the upper electrode.

To permit lengthwise adjustment of the *divid'er I88, the member is mounted on an intermediate plate I28. This intermediate plate I28 is connected to chute IIO by bolts I30. These bolts pass through longitudinal slots I32 in the intermediate plate I28. Thus the bolts I30 may be loosened and the plate I28 with divider I 08 adjusted longitudinally of chute III] to any de= sired position. i 3 I v The material segregated by divider I08 will pass down along the top of the divider and onto chute H and will be deposited by the chute i'n a receptacle I34 similar to receptacle I06. The edge of divider I08 should not project too fari'nto the electrostatic field, in order that the orientation and gradually decreasing intensity of the hem will not be influenced adversely by charges which may build up on the divider after contact with the charged particles. Thus the divider remains substantially at the edge of "the field. A

metallic divider may also be used, in order to minimize the accumulation Of charges from the of material which are attracted through the upper electrode and which pass downwardly on the upper surface of the upper electrode'will be collected in receptacle I42. At the same time, the material which remains within the electro static field between the upper and lower electrodes will be dischargedat the lower end of the electrostatic field and will be collected in recep tacl'es lfl fi and I34. Receptacle I06 will receive that portion of the materialwhich drops substantially directly and vertically from the discharge "edge 98 of the lower electrode, while r'e ceptacle I34 will receive an intermediate fraction of material depending on the longitudinal and perpendicular or angular adjustment of the divider plate I08 as discussed below.

In order to assist the feeding of the material downwardly along the lower stair step electrode 50, the supporting plate 51 on which the side supports 54 and Stand electrodes 50 and 52 are mounted are preferably vibrated or reciprocated. In theiorm shown in Fig. 2,- supporting-plate 51 The springs are mounted on the base H8 bf "2 suitable vibrator unit which is rastenea'to the lower-support I0 of fthe separator by bolts I50. An eleetromaghet I52 is mounted on-the sup: porting base I la while a magnetic armature I54 is rastenedtoone of the supporting springs I It at I56; The magnet is energized by irieans' of wires Its-and {I60 connected to a power source so that the armature I54 is reciprocated at a rapid rate; A rapid vibratory action will emordingly' be given to the support 51 and to the electrodes and-'52 which are mounted thereon. In the present case, this rapid vibration is in a direction having'components both perpendicular tc-and parallel to the general plane of electrodes 50 arid-52. I have also found, as discussed below, that sati'sfactory results may be obtained by-arapidvibration or reciprocation in a direction parallel to the edges of the steps 88 of lower electrode 50; i. 6:; a direction transversely of the electrostatic field, parallel to the plane of the electrodes, and perpendicular to the direction of feeding of the material.

with respect to the operation of the present machine, excellent results have been obtained by the use of the magnetic vibrators with a cycle alternating current source which gives a rreouenc'y oi vibration of 3600-cycles per minute. With the lower plate grounded, a negative potential of from 1500 to 3000 volts may be used for the purification of comminuted wheat stock when the up er and lower electrodesare spaced from one-half to one inch. In other words, a potential difference of between 1500 and 6000 volts per inch of separation is preferred. In this device, the steps of the individual electrades are inclined downwardly at about 7 below the horizontal. This angle is substantially less than the angle of repose of the material. The electrodes as a whole are inclined approximately 30 below the horizontal.

In Figs. 4, 5, and 6. another embodiment of the present invention has been shown. In this chibodiment, two pairs of electrodes according to the invention are superimposed in a single frame which is vibrated in the manner described below; The device includes a stationary main frame in eluding bottom frame members I14, side frame members. I16, and top frame members I18. Within this stationary frame the movable separrating unit is mounted. The separator includes side plates I and I82 which are connected by cross braces I84. Side plate I80 is suspended from the upper frame member I18 by resilient straps I80 which in this case are metallic. Similarly, side frame I82 is suspended from top frame members II8 by spring'straps I88. These straps are oriented as shown in Figs. 4 and 5 so that the frame members I80, I82 I84 may move or reciprocate in a direction substantially perpendicular to'the plane of the paper in Fig. 4, i. e., substa'ntially'laterally in the plane of the paper in Fig. 5-. Supported by the frame members I80 and I82, is a hopper I at the upper rear portion or the device. Hopper I90 may be supplied'from a suitable feed chute (not shown) which may be connected to the hopper'by a flexible conveyor sec:- tion in known manner. A feed gate I92 the hopper may be set to control the rate or feed of the material to be separated from the lower end of the hopper.

.This material is fed onto the lower electrode I94 or a pair of parallel inclined electrodes.- The ppeteelectrodee-Iilfi includes spaced overlapping strips of the type previously described, while the lower electrode I 94 includes steps or corrugations as already outlined.

The material which is projected through the upper electrode I96 and conveyed downwardly on its upper surface is received by a collecting plate I98 and directed into a suitable receptacle or feed chute 200. A fixed receptacle has been shown, for convenience, although a flexible spout is normally employed in a commercial installation to feed the separated material to the next apparatus in the mill fiow.

The material which remains in the field between electrodes I94 and I96 is separated into two cuts or flows by the divider edge 202. The material which passes above divider 292 is carried by a collecting plate or chute 264 into a collecting receptacle or further feed chute 206. The material which does not pass above the divider 262 but drops relatively directly from the lower electrode I 94 is carried by an inclined feed chute 208 to a second pair of electrode plates arranged on the frame members I80 and I82 below the first pair of electrodes. The second pair of electrodes includes a bottom electrode 2 I and an upper electrode 2 I2 of construction similar to the electrodes I94 and I96. Here again a collecting plate 2I4 receives the material which has been projected through the upper electrode 2I2 and directs that material into a collecting receptacle or further feed chute 2I6. A divider 2 I 8 separates the material leaving the lower electrode 2 I 6 into two fractions. The upper fraction is directed by collecting plate 226 into receptacle 222, while the lower fraction is directed by chute 224 into a further receptacle or chute 226.

With this device, the material which is fed from hopper I96 will ultimately be divided into five cuts or fractions collected at the receptacles 290, 266, 2I6, 222, and 226 respectively.

As already indicated, the resilient supports I86 and I88 permit vibration or reciprocation of the separating unit, including both sets of electrodes I94, I96, and 2H], 2 I2, in a direction substantially indicated by arrow 228 of Fig. 5. While any desired mechanism may be used to obtain the desired rapid vibratory reciprocation, Fig. shows a supporting bracket 230 on side plate I82, and a drive of the so-called Shaler type, designated as 232, mounted on bracket 23!). In general this drive is of the double eccentric type and includes two rotating unbalanced members 234 and 236, having their weighted portions 235 and 23? directly above each other at all times. The members 234 and 236 are rotated in opposite directions by suitable gearing. In this unit the arrangement of the weights is such that the vertical components of force exerted by one weight exactly counterbalance the vertical components exerted by the other. The resultant force exerted by the counter-rotating weights will b horizontal and will result in reciprocation of the separator unit back and forth in the direction of arrow 228. Such units are well known and need not be described further.

The unbalanced weight vibratory unit is driven by suitable belting 238 from an intermediate pulley 249, which in turn is connected by a belt 242 to a motor or other power s0urce'244. Motor 244 is mounted on a cross member 246 supported by the side frame members I16.

In this embodiment of the invention it will be noted that the direction of reciprocation or vibration is substantially parallel to the edges of the steps in the electrodes. As indicated in Fig. 6,

these electrodes are substantially similar to those of the embodiment previously described. Thus the upper electrode I96 includes spaced transverse strips 248 which are inclined downwardly to feed the material from one step to the next lower step. Each step has a riser or upwardly extending lip 250, the upper edge of which is spaced slightly below the end of the step above so as to leave an opening 252 between each pair of steps 248. The desired fraction of material carried by the lower electrode can then be projected through the openings 252 by application of a suitable potential difference to the electrodes.

Lower electrode I94 includes conveying step portions 256 separated by perpendicular risers 258. In this embodiment of the invention the risers of the lower electrode and the steps of the upper electrode are arranged in substantially one to one ratio so that for a given length of electrode, the same number of steps will be present in the upper electrode as in the lower one. This arrangement contributes a somewhat more uniform field than the construction shown in the previous embodiment in which the steps of the lower electrode were substantially shorter than those of the upper electrode. In this device the total length of one pair of the inclined electrodes is substantially eighteen inches in the direction of feed, with approximately twenty steps per foot. The individual steps are each fiveeighths of an inch wide, with a riser or perpendicular distance between steps of one-fourth of an inch. The perpendicular distance between electrodes is one-half inch. With a total electrode width of twenty-four inches, the machine can handle approximately six hundred pounds of stock per hour.

In this case the general plane of the electrodes is inclined at an angle of 30 to 35 below the horizontal, while the individual steps of the electrodes are inclined downwardly at 5 to 10.

Operation of the device of Figs. 4 through 6 is similar in principle to that of the previous embodiment. The electrodes are connected, as shown schematically in the drawing, so as to establish an electrostatic field between them of the desired intensity. In the connections shown, the same potential difference is applied to each pair of electrodes. Separate connections could be utilized to establish fields of different intensities at the respective electrode pairs.

As indicated in the introductory portions of this specification, Venetian blind upper electrodes have been used previously in combination with a lower inclined smooth plate electrode. Such devices have at best given a twofold separation, some of the particles being attracted through the upper electrode and carried downwardly on the upper surfaces of the transverse strips of the upper electrode, while the remaining material is discharged from the lower electrode. Corrugations have also been used in certain other electrode arrangements.

According to the present invention, however, the particular arrangement of the lower electrode, when combined with this upper electrode, has been found to give a surprising additional separation or third cut at the end of the electrostatic field. In the case of comminuted wheat stock, which contains pure bran particles, pure endosperm particles, and particles in which both bran and endosperm are attached in varying proportions, a relatively branny fraction may be attracted through the upper electrode and separated by means of receptacle I42. The remaining stock is conveyed downwardly along the edge of the lower electrode and is subjected to the vibrations imparted to this electrode. The combination of the steps or corrugations and the vibratory action appears to cause some stratification of the material so that relatively large particles of pure endosperm tend to hug the steps rather closely as indicated by the clear circles in Fig. 8. The pure branny particles tend to reach the top of the layer between the electrodes where they pass over the edges 94 of the steps at repeated intervals and are thus ready to be attracted when they are Subjected intermittently to the more intense electrostatic field at these points. One of these branny'particles (indi-- ated as a solid bla 'pa-rticle at I62 in Fi 3) may be considered for purposes of theoretical discussion, As the particle passes the stepedge .94, it is of course subject to the downward infiuence of gravity as indicated generally. by the arrow I64. The electrostatic field at this point, which is in general perpendicular to the plane of the electrodes, will exert an attractive force on the particle indicated by the arrow I66. e A por tion of the force of electrostatic attraction will tend to act vertically in opposition to the downward pull of gravity.

Another component of this electrostatic force may be exerted horizontally in the direction of feedto urge the particle to the right in the figure. At the same time the momentum which the particle has acquired in its movement down the lower electrode also tends to move the particle to the right. The sum of these forces tending to move the particle to the right is indicated generally by the arrow I68. The particle I62 will accordingly be subjected to a resultant force whose direction and magnitude depend on the direction and magnitude of the individual forces just mentioned. In some cases this resultant force will be in the general direction indicated by arrow H and will be sufficient to project the particle along the path of arrow I12 through one of the spaces 80 in the upper electrode. In other cases, the resultant force applied to the particle will be insufficient to cause such attraction and projection, If the electrostatic field has been adjusted so as to attract substantially pure branny particles, then those particles which include portions of both bran and endosperm (as indicated by the half shaded circles in Fig. 3) will tend to 'bedrawn more to the top of the layer of material passing through the field but will not be actually projected through the upper electrode.

The preliminary stratification resulting from the downward feeding of the material over the corrugations and steps in the presence of the electrostatic field and under the infiuenceof the vibrations applied to the supporting electrode 50 present the material to the diverging electrostatic field at the end of the electrodes in a condition in which the electrostatic field ofdiminishing intensity at the end of the electrodes is enabled to achieve a further separation of the material. relatively pure endosperm particles drop straight downwardly irom the dicsharge edge 98 and are relatively unaffected by the. field at this point. These particles are collected in receptacle I06. At the same time particles which include portions of both. b an. an endosperm t to e pr j ted out ardlyin the 'directionuof feeclo-f the material so that they clear th divider I08 and are led by chute I I!) to the intermediate receptacle 134. By

Thus, in the case of wheat. stock, the

. 10 suitable adjustment fthe divider I08 both longitudinally in the directionof feed and also perpendicularly to the general plane of the electrodes,

the operator may control the nature and degree I normally be projected farthest to the rightif the momentum and mass of the particles alone were to be considered.

While I do not wish to be bound by any particular theory as to the causes of thisadditional separation, it is my belief that the repeated rippling of the stock over the steps througha relatively long path of'feeding, in combination with the reciprocating motion of the steps, causes a mechanical lifting of thebranny or lighter par-'- ticles while the heavier endo'sperm particles hug, the steps very closely. In addition, there i an electrical lifting or stratification which may resultfrom passing the material over a series .of corrugations or steps at the edge of each of which theelectrostatic'field is somewhat more intense than at other points in the path. Thus the steps contribute both mechanically and electrically to the stratification of the material and to. the acquisition of. a substantially complete charge by each particle. It may be that the total charges acquired by the respective particles depend to some extent on the rate of acquisition of the charges and this in turn may be affected by the passage through the electrostatic field and through repeated areas of more intense field strength.

Furthermore, the separation which is obtained at the end of the electrodes appears to depend to some extent on the diverging electrostatic field and on the more horizontal orientation of the field at this point,.as well ason the fact that the upper electrode extends a substantial distance beyond'thelower electrode. The provision of the respect to each other in the longitudinal direction of feed, so that the material passes through a field of increasing or diminishing intensity as may be:

required by the particular problem encountered. The useof. the-term substantially parallel in the claims is intended to include such minor angular-variations.

In practice, myinvention has been found most satisfactory in the handling of comminuted wheat stocks which have not been too finely ground;

In other words, the separator may be used-as a middlings purifier andwill operate satisfactorily on the sizings, the coarse and fine first middlings and otherv middlings stock as distinguished from the finely powdered stocks wherein the particle size more nearly approachesthat-ofthe finished flour. Such dust-like or fine flour particlestend to form agglomerates which are not readily broken up and-which therefore prevent the'more precise separations, which'are possible withsizing andmiddl'ings stocks.

The apparatus' descrlbed above accomplishes the objects of the present invention and provides a useful and accurate device for purification of stocks in the flour milling field and also in other fields where precise separation is required, and particularly where the particles of material to be separated are all relatively non-conducting.

Certain features shown but not claimed in the present application are claimed in the copending application of William A. Brastad and Eli C. Gear, Serial No. 108,476, filed August 4, 1949.

Since minor variations and changes in the exact details of construction will be apparent to persons skilled in this field, it is intended that this invention shall cover all such changes and modifications as fall within the spirit and scope of the attached claims.

Now, therefore, I claim:

1. An electrostatic separator comprising substantially parallel inclined upper and lower electrodes, the upper electrode having a plurality of openings therein through which material attracted from the lower electrode may be projected onto the upper surface of the upper electrode and the lower electrode having on its upper surface a series of transverse steps down which the material to be separated may be fed, means for feeding a thin uniform stream of the material down across said steps between the electrodes, means for maintaining a diiference of potential between the electrodes, and means for collecting separately the material discharged from the respective electrodes. 7

2. An electrostatic separator comprising substantially parallel inclined upper and lower electrodes, the upper electrode having a plurality of openings therein through which the material attracted from the lower electrode may be projected onto the upper surface of the upper electrode and the lower electrode having on its upper surface a series of transverse steps down which the overlapping each other in stepwise formation and separated by transverse openings through which particles attracted from the lower electrode may be projected onto the upper surfaces of the strips and the lower electrode having on its upper surface a relatively large number of transversely extending corrugations down which the material to be separated may be fed and means for feeding a thin uniform stream of the material down across said corrugations between the electrodes.

6. An electrostatic separator comprising substantially parallel inclined upper and lower electrically conducting electrodes, the upper electrode having a plurality of openings therein through which material attracted from the lower electrode'may be projected onto the upper surface of the upper electrode and the lower electrode having on its upper surface a series of transverse steps down which the material to be separated may be fed, and means for rapidly vibrating the lower electrode as the material is fed along it.

7. An electrostatic separator according to claim 6 having means for rapidly vibrating both the upper and lower electrodes.

8. An electrostatic separator according to claim 6 in which the electrodes are generally inclined at an angle between and with respect to the horizontal, and in which the individual steps material to be separated may be fed, means for feeding a thin uniform stream of the material down across said steps between the electrodes, means for adjusting the perpendicular distance between the electrodes, and means for adjusting the relative position of the electrodes in the direction of feed, and thereby adjusting the relative orientation of said openings and steps.

3. An electrostatic separator comprising substantially parallel inclined upper and lower electrically conducting electrodes, the upper electrode having a plurality of openings therein through which material attracted from the lower electrode may be projected onto the upper surface of the upper electrode and the lower electrode having on its upper surface a series of transverse steps down which the material to be separated may be fed, means for feeding a thin uniform stream of the material down across said steps between the electrodes, the lower electrode having an extension at its lower end diverging downwardly and providing an extended electro static field which is more nearly horizontal than the field between the main portions of the electrodes.

4. An electrostatic separator according to claim 3 having a divider mounted at the lower end of theelectrodes, and means for adjustment of the divider both longitudinally of and perpendicularly to the plane of the electrodes.

5. An electrostatic separator comprising substantially parallel inclined upper and lower merality of downwardly inclined transverse strips of the lower electrode are inclined downwardly at an angle between 5 and 10.

9. An electrostatic separator according to claim 6 in which the vibration is in a direction having a component substantially perpendicular to the plane of the electrode.

10. An electrostatic separator according to claim 6 in which the vibration is in a direction substantially parallel to the edges of the transverse steps.

11. An electrostatic separator comprising substantially parallel upper and lower electrodes inclined downwardly in the direction of feed, each electrode comprising a series of overlapping steps separated by substantially perpendicular risers, the risers of the upper electrode having openings therein through which particles attracted from the lower electrode may be projected onto the upper surface of the upper electrode, and means for feeding a thin uniform stream of material down across the steps of the lower electrode and between the electrodes. I

12. An electrostatic separator comprising substantially parallel upper and lower electrodes inclined downwardly in the direction of feed, each electrode comprising a series of corrugations having substantially horizontal and vertical portions, the vertical portions of the upper electrode having openings therein through which particles attracted from the lower electrode may be projected onto the upper surface of the upper electrode, and means for feeding a thin uniform stream of material down across the corrugations of the lower electrode and between the electrodes.

13. An electrostatic separator comprising substantially parallel inclined upper and lower electrodes each of which comprises a series of downwardly inclined steps separated by risers, the risers of the'upper electrode having openings therein through which material attracted from the lower electrode may be projected onto the upper surface of the upper electrode, and means for feeding a thin uniform stream of material down across the steps of the lower electrode and between the electrodes.

14. An electrostatic separator according to claim 13 in which the upper and lower electrodes have the same number of steps per unit length.

15. An electrostatic separator according to v claim 13 in which the upper and lower electrodes have different numbers of steps per unit length. 16. An electrostatic separator according to claim 15 in which the lower electrode has more steps per unit length than the upper electrode.

17. An electrostatic separator comprising sub-- stantially parallel inclined upper and lower electrically conducting electrodes, the upper electrode having a plurality of openings therein through which material attracted from the lower electrode may be projected onto the upper surface of the upper electrode and the lower electrode having on its upper surface a series of transverse steps down which the material to be separated may be fed, the individual steps being inclined downwardly at an angle substantially less than that at which some portions of the material to be separated just begin to move under the influence of gravity, and means for rapidly vibrating the lower electrode and thereby feeding the material down across said steps.

18. An electrostatic middlings purifier comprising substantially parallel inclined upper and lower electrodes each of which comprises a series of downwardly inclined steps, the steps of the upper electrode being separated by openings through which a first portion of material attracted from the lower electrode may be projected onto the upper surface of the upper electrode, a divider at the lower end of the electrodes having an effective separating edge parallel to the plane of the electrodes and positioned in the path of material discharged from the field between the electrodes to separate the remaining material into upper and lower second and third portions respectively, means for feeding a thin uniform stream of the material down across the steps of the lower electrode and between the electrodes, and means for collecting separately the first, second and third portions.

19. An electrostatic middlings purifier according to claim 18 in which the divider comprises an inclined plate, a transverse shaft parallel to the edges of the steps and on which the plate is supported, and means for angular adjustment of the plate with respect to the axis of the shaft.

20. An electrostatic middling-s purifier comprising substantially parallel inclined upper and lower electrically conducting electrodes, the upper electrode having a plurality of openings therein through which material attracted from the low- 14 s er electrode may be projected onto the upper surface of the upper electrode and the lower electrode having on its upper surface a series of transverse steps down which the material to be separated may be fed, and means for feeding a thin uniform stream of the material down across the steps of the lower electrode and between the electrodes.

21. An electrostatic middlings purifier comprising a frame, a first set of substantially parallel inclined upper and lower electrodes mounted in the frame, a second set of similar electrodes mounted below the first set, the upper electrode of each set having opening-s through which material attracted from the lower electrode of the set may be projected onto the upper surface of the upper electrode, and the lower electrode of each set having on its upper surface a series of transversesteps down which material to be separated may be fed, means for feeding a thin uniform stream of the material down across the steps of the lower-electrode of the first set, means for collecting separately the portions of material discharged by the upper electrodes, a divider at the lower end of each set of electrodes fordividing the remaining material into upper and lower fractions, means for feeding the lower fraction from the first electrode in a thin uniform stream down across the steps of the lower electrode of the second pair of electrodes, and means for collecting separately the upper fraction of the first REFERENCES CITED The following references are of record in the file of this patent: I

UNITED STATES PATENTS Number Name Date 880,891 Lawson Mar. 3, 1908 1,020,063 Sutton Mar. 12, 1912 Gro e qrfiq s Dec. 2 

